1. Field of the Invention
The present invention relates to orthopedic fixation screws and methods and more particularly to such screws and methods in which a bone graft is anchored in a bore formed in a bone mass.
2. Description of the Related Art
The anterior cruciate ligament (ACL) is 25 mm-40 mm in length and is frequently injured in contact and other activities. Such injuries can cause instability in the knee to the extent that ACL reconstruction may be required.
The replacement of the ACL with the central third of the patellar tendon using a bone-tendon-bone graft is a known method for restoring knee stability. In this procedure, the central third of the patellar tendon and portions of bone at either end thereof are taken as a graft. A tunnel is bored in the distal femur and proximal tibia, i.e., where they join at the knee. The bone-tendon-bone graft is disposed with one bone segment in one of the tunnels and the other bone segment in the other tunnel. With the graft so disposed, each of the bone segments are anchored by screwing an interference screw into the tunnel between a tunnel wall and the bone segment thereby anchoring the segment in the tunnel.
Such procedure is illustrated and described in U.S. Pat. No. 4,927,421 to Goble et al. for process of endosteal fixation of a ligament. The Goble et al. method suffers from several disadvantages. First, the interference screw is cannulated, i.e., it has an axial bore for riding a guide wire into the bore. The wire must be inserted into the bore adjacent the bone graft before the screw can be installed. The guide wire prevents divergence of the screw as it is screwed into the space between the graft and the tunnel wall. A special driver, also having an axial bore for receiving the guide wire, must be provided to install the screw. Threading the wire through the bore is an additional surgical step, in itself undesirable, which has the potential for creating metal debris. In addition, the guide wires can bend or kink. The screw of the Goble et al. application provides an extremely steep taper at the leading end thereof which rapidly compresses the graft as the screw is installed.